This project was originally undertaken when our laboratory synthesized a unique membrane surface specific fluorescent phospholipid (1-acyl-2-(N-4-nitrobenzo-2-oxa-1,3-diazole)-aminocaproyl phosphatidylcholine) and utilized this compound as an indicator of the phase transition temperature of cultured human 21-trisomy fibroblasts. The results of these studies indicated a significantly higher transition temperature for the Down's cells than those found in normal cells. These results suggested that the 21-trisomy cell membranes exhibited architectural differences which might account for the symptoms of this syndrome. It was later discovered that cells derived from cultures of differing passage number exhibited different phase-transition curves. Consequently, membrane studies were carried out with material obtained from passage 7 or lower. The causative factor appears to be the total time cells are exposed to normal foetal calf serum. This observation may explain controversies arising between laboratories involving a number of measurements. We are presently comparing both resting and depolarizing potentials (using fluorescent techniques) in normal and 21-trisomy cell suspensions. Any differences noted in the electrical properties of the Down's cells may be related to their abnormal phase transition properties. We have recently synthesized a new highly fluorescent tag specific for the -COOH functional group. Membrane derived fatty acids will be analyzed at the picogram level with this reagent by both HPLC and GC/MS methods. In order to account for any fatty acids linked by vinylether bonds to spingomylin or phospholipids we have developed a highly fluorescent aldehyde specific (vinylether yields aldehyde) reagent. Further, since abnormal storage and/or reuptake of serotonin has been reported in these patients we have developed GS/MS methods which can detect picogram amounts of the alternate products of tryptophan metabolism. One of these compounds, tryptamine, is a known serotonin reuptake blocker in platelets. Consequently, high levels of these compounds in Down's tissue might explain the decreased amount of 5-HT.